A novel precision voltage reference using a micromechanical resonator

Abstract

This thesis describes the analysis and design of a precision voltage reference (PVR) based upon a micromechanical resonator. The precision voltage reference consists of two closed loop controllers and a nonlinear resonator. The oscillator loop maintains oscillations in the resonator. The phase locked loop is a frequency control loop that locks the resonator frequency to an external frequency. The micromechanical device consists of a pair of resonators that are electrostatically driven and sensed in their out-of-plane vibrational resonance mode. The oscillating proof masses move on flexure beams and the resonator is configured for use as a voltage controlled oscillator within the phase locked loop. The first order stiffness coefficient has an electrostatic component that reduces the frequency of oscillation with increasing bias voltage applied to the resonator. The resonator's frequency sensitivity to voltage is realized by the first order, bias voltage dependent stiffness coefficient. The input bias voltage to the voltage controlled oscillator is the precision voltage reference. A prototype PVR device was constructed and the PVR operation confirmed. Results between a first order design analysis, advanced modeling, and the prototype are in good agreement. The error model indicates the baseline design for the micromechanical PVR achieves a total voltage stability below 0.4 parts per million (ppm) with temperature control of 0.1°C.